Bolt Types

Why it has to be 316SS or Titanium

This is a huge subject (read more at The Bolting Bible and Crag Chemistry) but for the purposes of this site we will keep it super simple and tell you just what you need to know for bolting today.

Historically (up to 2010), we estimate 60% of climbing fixtures installed worldwide were made of 304-grade stainless steel, with 20% made of 316-grade stainless, and 20% something worse like zinc-plated or cadmium-plated (seen these gold fixed hangers littering Euro crags?). This has essentially been a gigantic worldwide metallurgy experiment and after many years the results are in, and the EN Standards body have spoken.

It's very simple:

• The latest EN959 Standard says use 316SS everywhere, and titanium for areas near the ocean (or any known high-corrosion environments).

• The use of 304SS (and lower) is restricted to indoor use only!

This means there are hundreds of thousands 304SS (and lower) fixings across cliffs worldwide that (at time of replacement) will need to be upgraded to 316SS or titanium.

• 👍 👍 Titanium

  • The best material - does not rust in any environment

• 👍 316 stainless steel

  • Works nearly everywhere but in certain seaside locations, titanium has proven to be the better choice.

  • Metric bolts are often stamped A4 (A2 means 304 - beware!)

  • Sometimes you will see a bolt stamped with 316L. 316L's lower carbon content imparts even better corrosion resistance than 316 and is essential for welded components.

• 👎 Duplex or PLX or HCR (high corrosion resistant) stainless (discontinued)

  • After many recorded failings of their 304SS products, the brand Fixe tried to produce something more corrosion resistant than 316SS. The short story is they failed and the products were discontinued in favour of 316SS, not before many of these found their way onto cliffs worldwide and there were several failures.

• 👎 304 stainless steel (still very common and actively sold - beware!)

  • Metric bolts are often stamped A2

• 👎👎 Galvanised (Zinc or Cadmium plated)

• 👎👎👎 Mild steel
  
  

Common types of corrosion

1. Galvanic corrosion (dissimilar metals)

   • If metals are touching, they need to be the same grade of stainless steel.

   • How to avoid? → Ensure bolts, washers and hangers are the same grade of stainless steel. Learn more.

2. Stress corrosion cracking (SCC)

   • Causes catastrophic failure of the steel.

   • How to avoid? → Place titanium in seaside environments. Learn more.

3. Sulphide stress cracking (SSC)

   • Similar catastrophic failure of the steel, but via a different root cause.

   • How to avoid? → Place titanium in seaside environments. Learn more.

Sure, they sold me 316SS, but how would I know?

Use a magnet. Cheap strong magnets can be found in the welding area of your local hardware store. We have now recorded several instances of supposedly 316SS name brand expansion bolts failing, and when tested, were found to be a lower grade of steel. If the hardware you plan to place is even slightly attracted to a magnet, do not use it. You will find titanium and true 316SS are non-magnetic. 304SS is slightly magnetic. Worse grades of steel are strongly magnetic. Learn more.

More info

• The Book of Metal (Bolting Bible) - https://hownot2.com/

• Crag Chemistry (Dave Reeve is assisting the UIAA form recommendations regarding stress corrosion cracking (SCC) and sulphate reducing bacteria (causing Suphide Stress Cracking - 'SSC') on coastal cliffs)

Galvanic corrosion due to dissimilar metals. Interestingly it's often the washer that's at fault! Use the magnet test on all components individually before sandwiching them together.

Stress cracking (either SSC or SCC) in Fixe 304 stainless steel ringbolt in Thailand.

Sold as a higher grade of stainless, this hanger cracked after only 2 years installed. It was traced back to a bad batch of steel used at time of manufacturing, however the magnet test would have prevented this!

Bolt Types and Worldwide Best-Practice (2025 update)

The bolt types below are a non-exhaustive list and are included as illustrative examples. There are obviously many types and many manufacturers.

Glue-in Ringbolts

Glue-in rings are widely regarded as the strongest and most durable type of climbing anchor. Designed to last decades even in harsh environments, they outperform other bolt types in both strength and resistance to wear. Their robustness makes them ideal for high-traffic routes.

That said, glue-in rings come with a few important considerations. They require more complex preparation than expansion bolts and need specific tools and materials to install properly. The rod is typically 10 mm in diameter, and the hole drilled must be slightly larger - usually 12 mm. A key requirement is recessing the eye of the ring into the rock. This isn’t just for aesthetics: it prevents the ring from twisting, which can compromise the glue bond over time.

Glue-in rings must be used with injection adhesives. Pre-filled glass capsules don’t contain enough glue to fully bond the bolt, especially in recessed placements. Because of this, installation requires a specialised glue gun and adequate curing time.

Historically, many glue-ins used in Australia were homemade, often by local route developers. However, with broader access to certified products, this practice is declining. Today, Safer Cliffs Australia recommends only using EN 959-certified commercial glue-in bolts to ensure consistent quality and safety.

Finally, surface preparation plays a critical role in the performance of glue-ins. Any contaminants - like grease or manufacturing residue - can weaken the bond between the glue and the metal. Ensuring the ring is clean and correctly recessed helps maintain long-term reliability without compromising usability (e.g., avoiding overly deep recesses that can interfere with carabiner function).

• Pro: Eye fits multiple carabiners and can be lowered off

• Pro: Bolt cannot be easily stolen or tampered with

• Pro: Good in soft rock

• Pro: Longest service life

• Con: More skill required to install than expansion bolts

• Con: Takes up to 24 hours before you can use

• Con: Harder to replace

• Con: Tools are expensive (caulking gun)

• Con: Likely to pull out without warning if placed incorrectly

Recommended brands/models

• Raumer

• Fixe

• Petzl

History lesson. Various types of ringbolts used from 1990-2010

1. Penrith 'rockpig' homemade ring from NSW

2. Rebolting NSW homemade ring

3. Arapiles Mountain Equipment commercial ring

4. Petzl commercial ring

5. Fixe commercial ring

A well-recessed, EN959 certified, 10mm ringbolt

Not recessed, and capsule glue. Bad.

Glue-in U-Bolts

Glue-in U-bolts are a distinctive anchor type commonly used in Australia, though they’re far less popular in most other parts of the world. Their appeal originally came from practicality: made from 10 mm 316 stainless steel rod, they required no welding and could be bent and installed with relatively basic tools. This made them one of the more affordable options for bolting steep terrain, particularly roofs.

Today, the widespread availability of commercial EN 959-certified ringbolts and U-bolts has shifted best practice away from homemade hardware. As a result, Safer Cliffs Australia now recommends using only commercially manufactured, certified U-bolts.

U-bolts require two drilled holes per unit, which introduces specific considerations. One potential hazard is that the spacing between the legs can allow certain carabiners to twist and unclip under load. To reduce this risk, a leg spacing greater than 45 mm is recommended.

One of the main advantages of U-bolts is their installation stability. They typically require light hammering to seat them in place, which helps hold the bolt in place while the glue cures - an especially useful trait when bolting in roofs or overhangs.

Proper surface preparation is also important. U-bolts should be thoroughly cleaned with soapy water or acetone to remove any surface contaminants or residues from manufacturing.

A final and critical note: it’s essential to drill both holes straight and to ensure that the U-bolt fits cleanly without excessive force. Forcing a poorly aligned U-bolt into place can introduce internal stress into the metal. Over time, this stress has been linked to stress corrosion cracking (SCC) - a potentially catastrophic failure mode, especially in marine or corrosive environments.

• Pro: Eye fits multiple carabiners and can be lowered off

• Pro: No welding required in manufacturing

• Pro: Two legs inherently resist torsion forces, no need for notching to recess

• Pro: Stays in overhangs when drying without sliding out of the placement

• Pro: Bolt cannot be easily stolen or tampered with

• Con: More skill required to install than expansion bolts

• Con: Takes up to 24 hours before you can use

• Con: The spacing between the legs can cause carabiners to unclip

• Con: Hammering U-bolts into uneven holes can damage the bolt

• Con: Tools expensive (caulking gun)

• Con: Likely to pull out without warning if placed incorrectly

Recommended brands/models

• Titan Climbing

• Fixe

Fixe Titanium U-bolt

Freshly installed Titan Climbing titanium glue-in U-bolt with Hilti RE-500 glue (don't panic - the pink colour fades with time, see this). It can also be camouflaged.

Homemade 316 stainless U-bolt with messy glue. A common sight on Australian sandstone cliffs. Safe, but gradually being phased out in favour of EN 959 compliant bolts. Also a good example of why being neat with glue matters.

Expansion Bolt with Fixed Hanger (hard rock only)

Note: It is the considered opinion of Safer Cliffs Australia that glue-in bolts should be favoured over expansion bolts unless there is a compelling case otherwise.

Expansion bolts are easy to place, strong and readily available. Expansion bolts work by either expanding or compressing - gripping the rock by pressing against the wall of the bolt hole. The expanding action creates friction between the anchor and the rock. For the bolt to pull out, the applied load has to overpower this coefficient of friction. Expansion bolts are expensive per placement, as you have to purchase a commercial hanger to use with the bolt.

• Pro: You can use them immediately after placing

• Pro: Almost foolproof to place

• Pro: Less tools to buy

• Pro: Hanger is replaceable

• Pro : Likely to show signs of working loose if in marginal placement

• Con: Bolt and hanger deforms after repeated falls

• Con: Hanger can be stolen and bolt tampered with

• Con: Bolt can loosen, hangers can spin

• Con: Rust (galvanic corrosion) can occur when two grades of stainless (i.e. bolt vs washer vs hanger) are forced together
  

Recommended brands/models for hard rock only:

• Ramset 12mmx75mm SS Hex-Head Dynabolt DP12075HSS

• Powers Flush Head Sleeve 12mm SS FHS1275SS

• Powers Power-Bolt Anchor 12mm SS RBHM1370SS

• Fixe 12mmx75mm Triplex SS Expansion

• Hilti 12mmx102mm SS HSL-G-R

Disadvantages of the 'Tru-bolt' style of expansion bolt

1. Cannot be easily extracted from the hole to allow for clean replacement without the use of specialised tools made for the purpose (various types listed on this page). Without special tools, must be cut off using a cordless grinder and then beaten back into hole and the hole patched with epoxy and camouflaged. Not great!

2. Because the thread sits exposed from the nut, it can foul the carabiner leading to dangerous orientation of the carabiner. There are many cases where this has led to a carabiner snapping (see pic).

3. Sideways forces on the hanger cause the nut to loosen. If the nut loosens completely, the hanger falls off and the climber has no protection. Because climbers (should, but) don't regularly check and tighten expansion bolts, many routes are missing hangers due to this issue.

We eliminate all these issues by placing flush head style expansions instead. Or better yet, glue-in bolts!

Components of Flush Head Sleeve Anchor (superior to Trubolts)

A Ramset 12mm Flush Head Dynabolt (DP12075HSS) with Fixe Hanger

Tru-bolt style expansion bolt. Popular due to easy placement, but not a great choice, see explanation

Snapped carabiner due to fouling on exposed Tru-bolt stud

Regular dynabolts (as opposed to Flush Heads) are unsuitable as the nuts easily unscrew. Do not use these.